Fluid Simulation is still low quality even with resolution of 250
For one thing, a resolution of 250 isn't that much. Everything will look crappy at that resolution. And as gandalf3 said, make sure your domain isn't unnecessarily large.

Setting subdivisions to 2 won't really improve your simulation in this case. Change it back to 0 (or 1, because of blender logic it is the same) and save some baking time.

For extra smoothing, use the smooth modifier. However, it may reveal holes in the fluid mesh, so make sure you check what's going on before you render.